1. Field of the Invention
This invention relates to an apparatus for separation of gas from gas-liquid mixtures and promoting droplet coalescence of different liquids in the gas-liquid mixture.
2. Description of Related Art
Liquid/gas separation and droplet coalescence are important aspects of crude oil processing, especially at the early stages of production from the well head. The main goal of separator vessels, typically located in a Gas Oil Separation Plant (“GOSP”), is to separate the fluids and obtain oil of satisfactory quality having reduced water and gas content. As the water cut increases, oil production from the separator vessel is adversely influenced.
U.S. Pat. No. 2,228,401 describes a centrifugal device for separating gases from oil in which liquid is forced under pressure through a conduit connected via a flange in a substantially tangential direction. Liquid enters the conduit and is subjected to centrifugal force, and liquid separates into the lower part of the conduit.
U.S. Pat. No. 4,070,168 describes an inlet assembly, for mounting within a separator vessel, in the form of a “snail shell” shape with a spiral side wall. Pressurized crude oil is delivered tangentially to the inner end of the spiral side wall. Gas is centrifugally separated in the central portion of the spiral, and liquids flow along the larger radius of the outer portion.
The apparatus described in U.S. Pat. Nos. 2,228,401 and 4,070,168 are used only to separate gas from liquid, and thus separate treatment is required if the liquid is a mixture of oil and water. In addition, these devices do not control the momentum of the liquid, thus potentially causing any oil and water mixtures to emulsify.
U.S. Pat. No. 4,778,494 discloses a fluid flow diverter and separator for use in separator vessels. The apparatus is a cyclone or centrifugal flow diverter structure, with an inner cylindrical wall and an outer cylindrical cap member surrounding the inner cylindrical wall. Under the swirling conditions, there is substantial separation of gas from the liquid, and partial separation or demulsification of the oil and water. In conditions of increased flow rates, the outer cap serves to minimize agitation of the partially separated or demulsified oil and water.
U.S. Pat. No. 6,458,191 discloses a separator inlet for use in a separator tank. The fluid is introduced into a spiral channel and flows in the housing to a centrally disposed outlet while releasing any gas in the stream. Fluid then flows downward through the outlet, and any remaining gas is captured by a funnel-shaped trap and conveyed to the surface.
U.S. Pat. No. 6,409,808 also discloses a separator inlet for use in a separator tank. Gases are discharged based on cyclonic effect, and the oil and water mixture is discharged into an oil layer in the separator tank. According to the patent, discharge into the oil layer promotes a more rapid and efficient separation of the oil and water, as compared to prior methods where the oil and water mixture was discharged in the water layer.
Related U.S. Pat. Nos. 7,001,448 and 6,773,492 disclose a system for separating an entrained liquid component from a gas stream, as improvements to a vortex tube cluster in the form of a tube-on-tube design. The improvement described is the use of a cylinder at the bottom of the vortex tube, in place of prior art diverter plates. The cylinder contains droplets and prevents re-entrainment of droplets in the gas phase. The references also describe two-phase liquids (oil and water), and states that the improved vortex tube configuration prevents propulsion of gas-laden liquid to the liquid outlet. Notably, these references do not disclose that the improved vortex tube improves droplet coalescence. Indeed, the references specifically describe use of a downstream liquid coalescing apparatus.
Therefore, a need exists for an apparatus that can be installed at the inlet of either a horizontal or vertical separator vessel to promote liquid-gas separation, and that further promotes coalescence of the different types of liquids, i.e., oil and water, to facilitate their separation in the vessel. Accordingly, it is an object of the present invention to improve existing separator vessels and maintain oil production levels even when the water cut increases, e.g., after years of production from the particular well.